1. Field of the Invention
The present invention relates to a tire vulcanizer for vulcanizing and patterning a tire within an openable and closable mold. More specifically, the present invention relates to a tire vulcanizer provided with a motor and a mechanical brake for controlling the lifting and lowering of a top mold mounting member that holds a top mold, and a brake control method therefor.
2. Description of the Related Art
A tire vulcanizer is a machine configured to vulcanize and pattern an unvulcanized green tire placed in a mold by heating from inside and outside the mold. Generally, the mold of the tire vulcanizer includes a two-piece mold divided into a top mold and a bottom mold. The top mold and bottom mold of the two-piece mold are held, respectively, on a top mold mounting member and a bottom mold mounting member, and opening and closing of the mold can be performed by lifting and lowering the top mold mounting member in a vertical direction relative to the bottom mold mounting member.
For example, a tire vulcanizer disclosed in Japanese Examined Patent Application Publication No. H1-24048 has a mechanical elevating means such as a screw shaft and a screw nut screwed to the screw shaft in such a manner as capable of being lifted and lowered, wherein the opening and closing of the mold can be performed by rotating the screw shaft with an electric motor to vertically lift and lower a top mold that moves up and down integrally with the mechanical elevating means relative to a bottom mold.
A tire vulcanizer disclosed in Japanese Patent Application Laid-Open No. 5-228938 includes an elevating shaft erected on the upper side of the center of an elevating stand through a fixture, and a female screw cylinder formed of a screw nut, a ball screw nut or the like, which is engaged with and inserted through the elevating shaft, wherein the opening and closing of the mold can be performed by rotating the female screw cylinder with a driving body to lift and lower the elevating shaft, thereby vertically lifting and lowering a movable top mold attached to the lower surface of the elevating stand relative to a fixed bottom mold.
In the process of vulcanizing green tire, the lifting and lowering of the top mold may be stopped in mid-course in case of, for example, loading or unloading a tire, emergency stop or the like. As the screw shaft or elevating shaft used as the elevating means, an efficient ball screw or the like is generally used in order to minimize the output of the motor or the like for rotating it. If such an efficient screw is used, particularly during lowering of the top mold, the top mold may not stop by powering off the motor due to the inertia of the motor and that of a rising and lowering part such as the top mold. Further, reverse fall of the top mold may occur during lifting of the top mold. Therefore, a mechanical brake such as an electromagnetic brake is attached to the conventional motor to stop the lifting and lowering of the top mold with the mechanical brake. Here, if abnormality such as breakage of the electromagnetic brake occurs during stoppage of the top mold, the brake on the top mold goes out, causing a problem such as collision with the bottom mold due to fall. Further, abnormality such as breakage of a driving mechanism (the motor or a power transmission unit for transmitting drive power of the motor) during the lifting and lowering of the top mold causes a problem such as fall of the top mold or breakage of a guide part for guiding the lifting and lowering of the top mold due to imbalanced load. However, the tire vulcanizes disclosed in the literatures described above have no countermeasures to abnormalities as described above.